Signaling the RNAi space remains a hot ticket, Arrowhead Research Corp. priced an underwritten offering of 5.5 million shares of common stock at $18.95 apiece, seeking to raise $104.225 million. The Pasadena, Calif.-based company granted the underwriters a 30-day option to purchase up to an additional 825,000 shares, potentially increasing the deal size by $15.6 million.